Snap to vertex or edge does not work
Although not 100% sure, I believe
1. I need to press and hold the Ctrl key while extruding.
2. I set the snap to option to Closest
3. I set the pivot point to active element


I did turn on "Automatically merge vertices moved to same location".  However, when I checked afterwards by clicking the remove doubles, 56 doubles were still removed.  So not sure how that is suppose to work.